[clang] [clang] Add -Wimplicit-fallthrough to -Wextra (PR #97926)

[Max Coplan via cfe-commits]

https://github.com/vegerot updated https://github.com/llvm/llvm-project/pull/97926

>From 9640f00fac2be5984b6a0ee2f7f917a58f7e53d8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Max=20=F0=9F=91=A8=F0=9F=8F=BD=E2=80=8D=F0=9F=92=BB=20Copl?=
 =?UTF-8?q?an?= <mchcopl at gmail.com>
Date: Sat, 6 Jul 2024 17:22:55 -0700
Subject: [PATCH] [clang] Add -Wimplicit-fallthrough to -Wextra

This patch adds -Wimplicit-fallthrough to -Wextra. GCC already includes it in -Wextra.

This patch also adds a test to check that -Wimplicit-fallthrough is included in -Wextra.

Note: This patch may regress performance when building with -Wextra.
This is because -Wextra requires forming a CFG for every function.
---
 clang/include/clang/Basic/DiagnosticGroups.td            | 1 +
 clang/test/Sema/fallthrough-attr.c                       | 1 +
 clang/test/SemaCXX/switch-implicit-fallthrough-macro.cpp | 1 +
 3 files changed, 3 insertions(+)

diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
index 19c3f1e043349..2a307679c9283 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -1067,6 +1067,7 @@ def Extra : DiagGroup<"extra", [
     StringConcatation,
     FUseLdPath,
     CastFunctionTypeMismatch,
+    ImplicitFallthrough,
   ]>;
 
 def Most : DiagGroup<"most", [
diff --git a/clang/test/Sema/fallthrough-attr.c b/clang/test/Sema/fallthrough-attr.c
index de50ebf39d42f..6cc19136f30a7 100644
--- a/clang/test/Sema/fallthrough-attr.c
+++ b/clang/test/Sema/fallthrough-attr.c
@@ -2,6 +2,7 @@
 // RUN: %clang_cc1 -fsyntax-only -std=gnu99 -verify -Wimplicit-fallthrough %s
 // RUN: %clang_cc1 -fsyntax-only -std=c99 -verify -Wimplicit-fallthrough %s
 // RUN: %clang_cc1 -fsyntax-only -std=c11 -verify -Wimplicit-fallthrough %s
+// RUN: %clang_cc1 -fsyntax-only -std=c11 -verify -Wextra %s
 // RUN: %clang_cc1 -fsyntax-only -std=c2x -DC2X -verify -Wimplicit-fallthrough %s
 
 int fallthrough_attribute_spelling(int n) {
diff --git a/clang/test/SemaCXX/switch-implicit-fallthrough-macro.cpp b/clang/test/SemaCXX/switch-implicit-fallthrough-macro.cpp
index 11df2cbfb53f0..cbbff1f1793b8 100644
--- a/clang/test/SemaCXX/switch-implicit-fallthrough-macro.cpp
+++ b/clang/test/SemaCXX/switch-implicit-fallthrough-macro.cpp
@@ -3,6 +3,7 @@
 // RUN: %clang_cc1 -fsyntax-only -verify -std=c++1z -Wimplicit-fallthrough -DCLANG_PREFIX -DCOMMAND_LINE_FALLTHROUGH=[[clang::fallthrough]] %s
 // RUN: %clang_cc1 -fsyntax-only -verify -std=c++1z -Wimplicit-fallthrough -DCOMMAND_LINE_FALLTHROUGH=[[clang::fallthrough]] %s
 // RUN: %clang_cc1 -fsyntax-only -verify -std=c++1z -Wimplicit-fallthrough -DCOMMAND_LINE_FALLTHROUGH=[[fallthrough]] -DUNCHOSEN=[[clang::fallthrough]] %s
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++1z -Wextra -DCOMMAND_LINE_FALLTHROUGH=[[fallthrough]] -DUNCHOSEN=[[clang::fallthrough]] %s
 
 int fallthrough_compatibility_macro_from_command_line(int n) {
   switch (n) {